Slide member and method for producing the slide member

ABSTRACT

A slide member having a slide surface slidable relative to a counterpart, including a base portion and a diamond-like carbon layer formed on a surface of the base portion and provided with a plurality of microrecesses on an outer surface thereof defining the slide surface. A method for producing the slide member, including subjecting a surface of a preform of the slide member to diamond-like carbon treatment to form a diamond-like carbon layer on an outer surface of the slide member, and forming a plurality of microrecesses on an outer surface of the diamond-like carbon layer by removing microparticles from the outer surface of the diamond-like carbon layer.

BACKGROUND OF THE INVENTION

The present invention relates to slide members such as valve lifters and rocker arms which transmit into engine valves, a reciprocation motion thereof produced by slide contact with a rotating cam surface of a drive cam mounted on a cam shaft of internal combustion engines. The present invention also relates to a method for producing the slide members.

As well known in the arts, intake valves and exhaust valves are driven to open and close intake and exhaust ports of the internal combustion engines by transmitting a rotating force of the drive cam mounted on the cam shaft thereto through valve lifters or rocker arms of a linear motion type. In this operation, an outer peripheral cam surface of the rotating drive cam comes into severe slide contact with a crown surface of the valve lifter or an upper end surface of the rocker arm via a lubricating oil film formed therebetween. The rotating force of the drive cam is transmitted as a reciprocation motion of the valve lifter or the rocker arm to the intake or exhaust valves. Thus, the valve-driving operation produces large friction loss between the drive cam and the crown surface of the valve lifter or the upper end surface of the rocker arm.

For the purpose of reducing the friction loss and thereby achieving efficient power transmission to improve fuel consumption and exhaust emission, there has been proposed a technology of a surface treatment of a slide surface of a slide member such as the above-described valve lifter.

Japanese Patent Application First Publication No. 2003-13710 describes such a technology of a surface treatment. In the conventional art, at least one of metal slide members coming into slide contact with each other, is provided on a slide surface thereof with dimples, and a slide surface of the other member is subjected to diamond-like carbon treatment (DLC treatment) to form a high-hardness surface having a hardness Hv of 1000 or more. The metal members are subjected to initial slide on each other so that the slide surfaces thereof except for the dimples are polished and smoothened, and simultaneously rises formed around the dimples upon production of the dimples are removed. Thus, the respective metal members have such a slide surface composed of a smooth surface portion and dimples distributed over the smooth surface portion. With the provision of the slide surface, projections present as roughness of the slide surfaces are prevented from contacting each other, and shearing resistance of oil is reduced. This results in reduction in slide resistance between the metal slide members.

SUMMARY OF THE INVENTION

However, in the above-described surface treatment of the conventional art, since the slide surfaces of the metal slide members except for the dimples are polished and smoothened by the initial slide motion therebetween simultaneously with removal of the rises around the dimples as described above, the rises around the dimples undergo plastic deformation toward an inside of the respective dimples upon the polishing, to thereby reduce a volume of the respective dimples. This causes problems such as unsatisfactory retention of a lubricating oil in the respective dimples and insufficient formation of an oil film between the metal slide members, thereby failing to effectively prevent occurrence of abrasion thereof.

An object of the present invention is to solve the above-described problems in the technology of the conventional art and to provide a slide member having a slide surface capable of reducing slide resistance between the slide member and a counterpart and allowing retention of a lubricating oil to thereby form an oil film therebetween.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

According to one aspect of the present invention, there is provided a slide member having a slide surface slidable relative to a counterpart under condition that a lubricating oil is supplied between the slide member and the counterpart, the slide member comprising:

-   -   a base portion; and     -   a diamond-like carbon layer formed on a surface of the base         portion and provided with a plurality of microrecesses on an         outer surface thereof which defines the slide surface.

According to a further aspect of the present invention, there is provided a slide member having a slide surface slidable relative to a cam so as to open and close an engine valve of an internal combustion engine under condition that a lubricating oil is supplied between the slide member and the cam, the slide member comprising:

-   -   a base portion; and     -   a diamond-like carbon layer formed on a surface of the base         portion and provided with a plurality of microrecesses on an         outer surface thereof which defines the slide surface.

According to a still further aspect of the present invention, there is provided a method for producing a slide member having a slide surface slidable relative to a counterpart under condition that a lubricating oil is supplied between the slide member and the counterpart, the method comprising the steps of:

-   -   subjecting a surface of a preform of the slide member to         diamond-like carbon treatment to form a diamond-like carbon         layer on the surface of the preform; and     -   forming a plurality of microrecesses on an outer surface of the         diamond-like carbon layer by removing microparticles from the         outer surface of the diamond-like carbon layer to thereby         provide the slide member with the slide surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view of a valve lifter according to a preferred embodiment of the present invention.

FIG. 1B is a vertical cross section of the valve lifter shown in FIG. 1A.

FIG. 2 is a cross section of a valve operating apparatus of an internal combustion engine to which the valve lifter of the preferred embodiment is applied.

FIG. 3 is a microphotograph showing microrecesses formed on a diamond-like carbon layer on a crown surface of the valve lifter at an area ratio of about 5% by brush-lapping in experiments.

FIGS. 4 and 5 are microphotographs respectively showing microrecesses formed on a diamond-like carbon layer on a crown surface of the valve lifter at an area ratio of about 20 to 30% by brush-lapping in experiments.

FIG. 6 is a microphotograph showing microrecesses formed on a diamond-like carbon layer on a crown surface of the valve lifter at an area ratio of about 60% by brush-lapping in experiments.

FIG. 7 is a diagram showing a characteristic curve showing a relationship between the friction resistance and the area ratio of the microrecesses.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the slide member and the method for producing the slide member, according to the present invention, will be described in detail below by referring to the accompanying drawings. The slide member has a slide surface slidable relative to a counterpart under condition that a lubricating oil is supplied between the slide member and the counterpart. In the embodiment, the slide member is used as a valve lifter in an internal combustion engine, which has a slide surface slidable relative to a cam so as to open and close an engine valve of the internal combustion engine.

Referring now to FIG. 2, there is shown a valve operating apparatus of an internal combustion engine in which the embodiment of the valve lifter according to the present invention is used. The valve operating apparatus includes intake valve 2 and exhaust valve 3 operative to open and close combustion chamber-side open ends of intake port 1 a and exhaust port 1 b, respectively, which are formed on an inside of cylinder head 1. Intake-side and exhaust-side camshafts 4, 4 are rotatably supported on an upper end portion of cylinder head 1 through a bearing. Drive cams 5 and 6 are integrally formed on an outer periphery of respective camshafts 4, 4. Valve lifters 7 and 8 as the slide members are slidably supported in small-diameter bores 1 c and 1 d of cylinder head 1, respectively. Valve lifters 7 and 8 come into slide contact with drive cams 5 and 6 as counterparts via a lubricating oil film formed therebetween, respectively. Valve lifters 7 and 8 are operative to convert a rotating force of drive cams 5 and 6 into a reciprocation motion thereof and transmit the reciprocation motion to intake valve 2 and exhaust valve 3.

Intake valve 2 and exhaust valve 3 are slidably supported in cylinder head 1 through cylindrical valve guides 9 and 10 fixed on cylinder head 1. Intake valve 2 and exhaust valve 3 are biased in a closing direction thereof by valve springs 12 and 13 fitted between spring retainers 11, 11 and bottom surfaces of respective bores 1 c and 1 d.

Camshafts 4, 4 are rotated by a rotational driving force transmitted thereto from a crankshaft, not shown, via a timing chain connecting a drive sprocket and a driven sprocket. Upon rotation of camshafts 4, 4, drive cams 5 and 6 fitted thereon are rotated integrally therewith so as to move intake valve 2 and exhaust valve 3 in an opening direction thereof.

Drive cams 5 and 6 may be made of chilled cast iron and have a rain droplet shape. Drive cams 5 and 6 are formed on outer peripheral surfaces thereof with cam surfaces 5 a and 6 a that come into slide contact with valve lifters 7 and 8, respectively. Cam surfaces 5 a and 6 a may be super-finished, for example, by polishing, and then processed into a desired smoothened surface by shot blasting.

Each of valve lifters 7 and 8 has a same structure. Referring to FIGS. 1A and 1B, only intake-side valve lifter 7 is explained for the sake of convenience. As shown in FIGS. 1A and 1B, valve lifter 7 includes a base portion including crown portion 14 and skirt portion 15 integrally formed with crown portion 14, and diamond-like carbon layer 17 formed on crown portion 14 of the base portion. Specifically, the base portion is made of an iron-based metal material and has a one-open ended hollow cylindrical shape including a circular upper wall serving as crown portion 14, and a cylindrical circumferential wall that extends downwardly from an outer circumferential periphery of the upper wall and serves as skirt portion 15.

Crown portion 14 has crown surface 14 a on an outer surface thereof, which is formed into a slightly spherical shape, i.e., an outwardly and upwardly swelled shape as viewed in FIG. 1B. Crown portion 14 further includes generally cylindrical boss 14 b integrally formed therewith. Boss 14 b projects inwardly from a center of an inner surface of crown portion 14 and comes into abutment to a stem end of intake valve 2. Also, crown portion 14 is formed with oil hole 16 at a predetermined outer peripheral position thereof. Oil hole 16 is in the form of a through hole and serves for introducing a lubricating oil attached onto crown surface 14 a to an inside of valve lifter 7 therethrough.

Diamond-like carbon layer 17 is formed on crown surface 14 a of crown portion 14. Diamond-like carbon layer 17 covers an entire area of crown surface 14 a and serves as a high-hardness surface treatment layer. Diamond-like carbon layer 17 is formed by subjecting crown surface 14 a to diamond-like carbon treatment. Diamond-like carbon layer 17 is provided with a plurality of microrecesses on an outer surface thereof defining a slide surface of valve lifter 7 which is slidable on cam surface 5 a of drive cam 5 under condition that a lubricating oil is supplied between the outer surface of diamond-like carbon layer 17 and cam surface 5 a. The slide surface, namely, the outer surface of diamond-like carbon layer 17 comes into slide contact with cam surface 5 a of drive cam 5 via the lubricating oil film formed therebetween. The microrecesses are formed by subjecting the outer surface of diamond-like carbon layer 17 to lapping treatment as explained later. The microrecesses have an area ratio of about 5 to 30% on the basis of an entire area of the slide surface, namely, the entire area of crown surface 14 a. The area ratio of the microrecesses is preferably within the range of 20 to 30%. The respective microrecesses have a maximum length of 0.1 to 5 μm.

A method of producing valve lifter 7 as the slide member, according to the present invention, will be explained hereinafter. First, a preform of valve lifter 7 is prepared in the following manner. An iron-based metal material is cold-forged to be formed into the preform of valve lifter 7 which has the one-closed ended cylindrical shape as explained above. The thus-produced preform has a basic shape of valve lifter 7 which includes crown portion 14 and skirt portion 15.

Next, inner and outer surfaces of crown portion 14 and skirt portion 15 of the preform are surface-treated. Crown portion 14 is drilled at a predetermined outer peripheral position thereof to form oil hole 16. Oil hole 16 may be formed upon the above-described cold forging of the preform.

Successively, the preform is subjected to heat treatment such as carburizing, carbonitriding and nitriding. Then, an outer peripheral surface of boss 14 b of crown portion 14 is polished to ensure alignment with an outer diameter of the stem end of intake valve 2. Similarly, an outer peripheral surface of skirt portion 15 is polished to ensure accuracy of slide contact with an inner periphery of bore 1 c of cylinder head 1.

Then, crown surface 14 a of crown portion 14 is super-finished into a roughness of about 0.1 μm, and an outer peripheral portion of crown portion 14 is subjected to lapping with abrasive particles, barreling or shot blasting to form a roundness R of about 0.02 μm.

Thereafter, the preform is placed in a furnace and washed therein, and then crown surface 14 a is subjected to diamond-like carbon treatment to form thereon diamond-like carbon layer 17 having a high hardness.

Subsequently, diamond-like carbon layer 17 covering crown surface 14 a is brush-lapped with diamond abrasive particles to remove a predetermined amount of microparticles (molecules) from an outer surface thereof such that a plurality of microrecesses 18 as shown in FIGS. 3 and 4 are formed thereon at an area ratio of about 5 to 30% on the basis of an entire area of the outer surface of diamond-like carbon layer 17, namely, the entire area of crown surface 14 a. In other words, the predetermined amount of microparticles is removed from the outer surface of diamond-like carbon layer 17 so as to control a ratio of a sum of areas occupied by microrecesses 18 on the basis of the entire area of the outer surface of diamond-like carbon layer 17 within the range of about 5 to 30%. As a result, diamond-like carbon layer 17 is provided with microrecesses 18 having the area ratio of about 5 to 30% on the basis of the entire area of the outer surface of diamond-like carbon layer 17, i.e., the entire area of crown surface 14 a. Meanwhile, the process for removal of the microparticles (molecules) may be conducted by barreling or shot blasting.

Upon the brush-lapping treatment for removing microparticles from the outer surface of diamond-like carbon layer 17 to thereby form the plurality of microrecesses 18, the present inventors have performed experiments to examine a relationship between the area ratio of microrecesses 18 and the frictional resistance between the outer surface of diamond-like carbon layer 17 covering crown surface 14 a and cam surface 5 a.

The experiments were respectively conducted in the case without lapping, the case where the area ratio of microrecesses 18, hereinafter referred to as the recess ratio, was about 5% as shown in FIG. 3, the case where the recess ratio was about 20 to 30% as shown in FIGS. 4 and 5, and the case where the recess ratio was about 60% as shown in FIG. 6. The results of the experiments are shown in FIG. 7.

In FIG. 7, reference character A denotes the frictional resistance caused in the case without lapping, namely the case where no microrecesses were formed on diamond-like carbon layer 17. Reference character B denotes the frictional resistance caused in the case where the recess ratio was about 5% as shown in FIG. 3. Reference character C denotes the frictional resistance caused in the case where the recess ratio was about 20 to 30% as shown in FIGS. 4 and 5. Reference character D denotes the frictional resistance caused in the case where the recess ratio was about 60% as shown in FIG. 6, respectively. As shown in FIG. 7, it was confirmed that, in the case without lapping, the frictional resistance W (rad) was 1, whereas in the cases where the recess ratios were about 5% and 20-30%, the frictional resistance W (rad) was reduced to near 0.8. Further, it was confirmed that in the case where the recess ratio was about 60%, the frictional resistance W (rad) was on the contrary increased to 1 or more.

Consequently, it was confirmed that when microrecesses 18 have the recess ratio of about 5 to 30%, the frictional resistance was reduced. Further, it was confirmed that the recess ratio was preferably in the range of 20 to 30% because the frictional resistance was minimized in this range.

As a result of these experiments, it was also confirmed that when respective microrecesses 18 had a maximum length of 0.1 to 5 μm, the frictional resistance was low, and retention of the lubricating oil in each microrecess 18 was most enhanced.

As described above, in this embodiment, crown surface 14 a of crown portion 14 of the preform of valve lifter 7 is subjected to diamond-like carbon treatment to form diamond-like carbon layer 17 having a high hardness thereon, and then subjected to lapping to form microrecesses 18 on diamond-like carbon layer 17 at the area ratio of about 5 to 30% on the basis of the entire area of crown surface 14 a. With the provision of diamond-like carbon layer 17 with microrecesses 18 on crown surface 14 a, the frictional resistance between cam surface 5 a and the slide surface of valve lifter 7, namely, the outer surface of diamond-like carbon layer 17 covering crown surface 14 a, can be reduced.

Further, since microrecesses 18 always retain a sufficient amount of lubricating oil therein, an oil film can be suitably formed between cam surface 5 a and the outer surface of diamond-like carbon layer 17 covering crown surface 14 a. This further reduces the frictional resistance between cam surface 5 a and the outer surface of diamond-like carbon layer 17 on crown surface 14 a upon the relative sliding motion thereof, to thereby enhance abrasion resistance of crown surface 14 a.

Therefore, even though cam surface 5 a of cam 5 has dimples thereon as observed conventionally or has no dimples thereon, the excellent effect can be attained by microrecesses 18 provided on diamond-like carbon layer 17 on crown surface 14 a of valve lifter 7.

In addition, in this embodiment, respective microrecesses 18 were formed such that the maximum length thereof fell within the range of 0.1 to 5 μm. Since microrecesses 18 have the maximum length of 0.1 to 5 μm, the frictional resistance between cam surface 5 a and the outer surface of diamond-like carbon layer 17 on crown surface 14 a can be reduced, and simultaneously a sufficient amount of lubricating oil can be retained in microrecesses 18.

Further, since cam surface 5 a can be formed into a smoothened surface, for example, with no dimples nor swelled portions, occurrence of contaminants such as abrasion powder produced by surface abrasion that is caused due to increase in contact pressure upon initial slide contact with valve lifter 7 can be effectively prevented.

Also, upon machining valve lifter 7, since the microparticles (molecules) are removed from the outer surface of diamond-like carbon layer 17 on crown surface 14 a, microrecesses 18 can be readily formed on diamond-like carbon layer 17.

In this embodiment, the microparticles are removed by a so-called brush-lapping process, microrecesses 18 are surely formed, and the removal thereof can be facilitated. Meanwhile, the lapping process may be conducted by blasting. In such a case, the same effect as that of the brush-lapping can be obtained by the blasting. The blasting method is described in U.S. Patent Application Publication No. U.S. 2004/0192567 A1 by Kenji Yamashita, the entire contents of which is hereby incorporated by reference.

The slide member of the present invention has the following effects. The slide member having the diamond-like carbon layer with the microrecesses exhibits an increased hardness to thereby be prevented from being readily deformed. As a result, the diamond-like carbon layer formed with the microrecesses exhibits a reduced slide resistance to the counterpart. In addition, since a suitable amount of a lubricating oil is received in the microrecesses, a sufficient oil film is always formed between the slide surface of the slide member and the surface of the counterpart, thereby improving an abrasion resistance thereof.

With the provision of the plurality of microrecesses on the outer surface of the diamond-like carbon layer of the slide member according to the present invention, irrespective of whether or not the counterpart is formed on the surface thereof with dimples as conventionally, the above effects can be always attained by the microrecesses.

Further, if the counterpart has a smoothened surface having no dimples nor swelled portions and coming into slide contact with the slide member of the present invention, occurrence of contaminants such as abrasion powder produced by surface abrasion that is caused due to increase in contact pressure upon initial slide contact with the slide member can be effectively prevented.

Further, the area ratio of the microrecesses provided on the diamond-like carbon layer of the slide member according to the present invention is within the range of about 5 to 30% on the basis of an entire area of the slide surface, so that the frictional resistance of the slide member against the counterpart can be minimized. In contrast, if the area ratio of the microrecesses is out of the above-specified range, the frictional resistance therebetween tends to be increased.

Further, the maximum length of the respective microrecesses on the slide surface of the slide member according to the present invention is adjusted to the range of 0.1 to 5 μm. As a result, the frictional resistance between the slide member and the counterpart can be reduced, and a sufficient amount of the lubricating oil is retained in the microrecesses.

Further, in the slide member according to the present invention which has the slide surface slidable relative to a cam so as to open and close an engine valve of an internal combustion engine, the base portion of the slide member is covered with the diamond-like carbon layer provided with the microrecesses on the outer surface thereof defining the slide surface of the slide member. With the provision of the diamond-like carbon layer with the microrecesses, even when the lubricating oil tends to be splashed off from the slide surface and thereby cause abrasion of the slide surface during rotating or pivotal movement of the cam provided on the camshaft of the internal combustion engine, the frictional resistance between the slide surface and the cam can be reduced. Further, since a sufficient amount of the lubricating oil is retained in the microrecesses, formation of a suitable oil film between the slide surface and the cam can be ensured, thereby effectively preventing the slide surface from suffering from severe abrasion.

In the above-described embodiment of the present invention, the valve lifter acts as the slide member, and the crown surface of the crown portion of the valve lifter is covered with the diamond-like carbon layer provided with the microrecesses on the outer surface thereof defining the slide surface of the valve lifter. With the provision of the diamond-like carbon layer having the microrecesses, the valve lifter can attain the same effects as explained above.

In the above-described method for producing a slide member having a slide surface slidable relative to a counterpart, according to the present invention, a surface of the preform is subjected to diamond-like carbon treatment to form the diamond-like carbon layer thereon, and then a plurality of microrecesses are formed on an outer surface of the diamond-like carbon layer by removing microparticles (molecules) from the outer surface of the diamond-like carbon layer to thereby provide the slide member with the slide surface. By subjecting the surface of the preform to the diamond-like carbon treatment, the surface of the preform is covered with the diamond-like carbon layer having a high hardness to thereby be prevented from being readily deformed. Further, by removing the microparticles, the microrecesses can be readily formed on the diamond-like carbon layer. Since a lubricating oil is retained in the microrecesses, formation of an oil film between the slide surface of the slide member and the counterpart can be ensured to thereby reduce the frictional resistance of the slide member against the counterpart. This enhances abrasion resistance of the slide member.

In addition, a predetermined amount of microparticles is removed such that the microrecesses are formed at an area ratio of about 5 to 30% on the basis of an entire area of the outer surface of the diamond-like carbon layer which defines the slide surface of the slide member. By controlling the area ratio of the microrecesses to the above-specified range, the frictional resistance of the slide member against the counterpart can be considerably reduced and the abrasion resistance of the slide member can be further improved.

Further, in the above-described method according to the present invention, microparticles are removed by a so-called brush-lapping from the outer surface of the diamond-like carbon layer. Therefore, the microrecesses can be surely formed on the outer surface of the diamond-like carbon layer, and the microparticles removing work can be facilitated.

Further, in the method according to the present invention, microparticles may be removed by blasting as described above. In this case, the microrecesses can be surely formed on the outer surface of the diamond-like carbon layer, and the microparticles removing work can be facilitated.

Furthermore, in the above-described method according to the present invention, microparticles are removed such that the microrecesses having the maximum length of 0.1 to 5 μm are formed on the outer surface of the diamond-like carbon layer. By controlling the maximum length of the microrecesses to the above-specified range, the frictional resistance of the slide member against the counterpart can be reduced, and the retention of the lubricating oil in the microrecesses can be improved.

The present invention is not limited to the above preferred embodiment, and can also be applied to exhaust-side valve lifter 8 as shown in FIG. 2, as well as parts other than the valve lifters such as rocker arms and other metal slide members.

This application is based on a prior Japanese Patent Application No. 2004-187187 filed on Jun. 25, 2004, the entire contents of which is hereby incorporated by reference.

Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A slide member having a slide surface slidable relative to a counterpart under condition that a lubricating oil is supplied between the slide member and the counterpart, the slide member comprising: a base portion; and a diamond-like carbon layer formed on a surface of the base portion and provided with a plurality of microrecesses on an outer surface thereof which defines the slide surface.
 2. The slide member as claimed in claim 1, wherein the counterpart has a smoothened surface coming into slide contact with the slide member.
 3. The slide member as claimed in claim 1, wherein the microrecesses are formed at an area ratio of about 5 to 30% on the basis of an entire area of the slide surface.
 4. The slide member as claimed in claim 1, wherein the microrecesses have a maximum length of 0.1 to 5 μm.
 5. A slide member having a slide surface slidable relative to a cam so as to open and close an engine valve of an internal combustion engine under condition that a lubricating oil is supplied between the slide member and the cam, the slide member comprising: a base portion; and a diamond-like carbon layer formed on a surface of the base portion and provided with a plurality of microrecesses on an outer surface thereof which defines the slide surface.
 6. The slide member as claimed in claim 5, wherein the slide member is a valve lifter in an internal combustion engine, the base portion including a crown portion of the valve lifter, the diamond-like carbon layer being formed on a crown surface of the crown portion, the plurality of microrecesses being provided on the crown surface.
 7. The slide member as claimed in claim 6, wherein the microrecesses are formed at an area ratio of about 5 to 30% on the basis of an entire area of the crown surface.
 8. The slide member as claimed in claim 6, wherein the microrecesses have a maximum length of 0.1 to 5 μm.
 9. The slide member as claimed in claim 6, wherein the valve lifter is made of an iron-based metal material.
 10. The slide member as claimed in claim 6, wherein the crown surface is formed into a slightly spherical shape.
 11. The slide member as claimed in claim 6, wherein the crown portion is formed with an oil hole at a predetermined outer peripheral position thereof.
 12. The slide member as claimed in claim 6, wherein the cam is made of chilled cast iron.
 13. A method for producing a slide member having a slide surface slidable relative to a counterpart under condition that a lubricating oil is supplied between the slide member and the counterpart, the method comprising the steps of: subjecting a surface of a preform of the slide member to diamond-like carbon treatment to form a diamond-like carbon layer on the surface of the preform; and forming a plurality of microrecesses on an outer surface of the diamond-like carbon layer by removing microparticles from the outer surface of the diamond-like carbon layer to thereby provide the slide member with the slide surface.
 14. The method as claimed in claim 13, wherein the step of removing the microparticles is conducted by brush-lapping.
 15. The method as claimed in claim 13, wherein the step of removing the microparticles is conducted by blasting.
 16. The method as claimed in claim 13, wherein at the step of removing the microparticles, the microrecesses having a maximum length of 0.1 to 5 μm are formed on the outer surface of the diamond-like carbon layer.
 17. The method as claimed in claim 13, wherein the slide member is the valve lifter, the preform being formed by cold-forging an iron-based metal material to form the preform into a basic shape of the valve lifter.
 18. The method as claimed in claim 17, wherein the preform is subjected to heat treatment after being formed into the basic shape of the valve lifter.
 19. The method as claimed in claim 18, wherein the preform is subjected to polishing after the heat treatment.
 20. The method as claimed in claim 19, wherein the preform is washed after the polishing, and then the surface of the preform is subjected to the diamond-like carbon treatment.
 21. The method as claimed in claim 13, wherein at the step of removing the microparticles, a predetermined amount of the microparticles is removed such that the microrecesses are formed at an area ratio of about 5 to 30% on the basis of an entire area of the outer surface of the diamond-like carbon layer. 